1. Field of the Invention
The present invention relates to rotation detection in a speed reduction mechanism using a planet gear mechanism in a drive force transmission mechanism or an apparatus using same.
2. Description of the Related Art
Various drive force transmission mechanisms provided with the differential gear mechanism using a planet gear disclosed, for example, in U.S. Pat. No. 5,640,636 have been proposed to obtain a high deceleration ratio in a compact space.
In speed reduction mechanisms achieved through a differential gear mechanism using a planet gear, however, it is difficult to assure a space for the because the gears occupy most of the space within the deceleration unit. Even assuming the detection member is installed, the deceleration unit is disadvantageously enlarged by an amount equal to the size of the detection member.
Furthermore, when rotation detection is accomplished at fine resolution outside the speed reduction mechanism achieved through a differential gear mechanism, the number of parts used increases which is a great demerit from the perspectives of cost and space due to the need to add an acceleration transmission system separated from the output shaft of the speed reduction mechanism, or arrange the detection member on the motor shaft on the side opposite the deceleration unit. The detection accuracy is disadvantageously reduced by gear backlash particularly when an acceleration transmission system is added.